Method, apparatus and program for the automatic processing of blood pressure signals

Abstract

The invention concerns an automated method, a system and means for processing the blood pressure from a detected pressure signal, the method operating in the time domain to determine a value (RES) connected to the energy efficiency of the monitored biological system.

1 . A method for automatic processing of blood pressure signals, the method comprising at least the following steps:
 A. sampling a detected pressure signal for one or more heartbeats, each heartbeat starting at an initial instant coinciding to that of an initial diastolic pressure and ending at a final instant coinciding to that of subsequent diastolic pressure and comprising a dicrotic point, each heartbeat having a systolic phase comprised between the initial diastolic point and the dicrotic point;   B. automatically analyzing and discriminating a morphology of the sampled pressure signal for each heartbeat, determining an instant and pressure value of one or more characteristic points of the pressure signal selected from one or more of a point of initial diastolic blood pressure, a point of systolic pressure, a dicrotic point and one or more resonance points, each of which occurs when a second derivative of the pressure signal has a relative maximum, wherein at least a characteristic point of the pressure signal belongs to the systolic phase of the heartbeat and is different from the point of initial diastolic pressure; and   C. for each heartbeat determining an energy efficiency value through the following sub-steps:
 determining a direct dynamic pressure wave impedance for each of said one or more characteristic points belonging to the systolic phase of the heartbeat into consideration with an exception of the point of initial diastolic pressure, said direct dynamic pressure impedance being given by a ratio between a value of the pressure signal in the characteristic point and a distance of the instant from the initial instant of the heartbeat into consideration, and determining an impedance of a direct pressure wave by adding with alternating signs the values of the dynamic direct impedances ordered according to a direct temporal order starting from the initial instant of the heartbeat into consideration up to the dicrotic instant, applying a positive sign to the first dynamic direct impedance according to the direct temporal order; 
 for each of said one or more characteristic points determining a dynamic reflected impedance that is given by the ratio between the pressure at the characteristic point and the distance of the respective instant from the instant of a final beat, and determining the value of an impedance of reflected waves of pressure is obtained by adding the dynamic impedances with alternating signs of the second set of points thus determined, sorted according to a reverse temporal order starting from the instant of the final beat to the instant of the initial diastolic pressure, giving a positive sign to the first dynamic impedance according to the reverse temporal order; and 
 determining said energy efficiency as the ratio between the impedance of the direct wave pressure and the impedance of the reflected waves. 
   
     
     
         2 . A method according to  claim 1 , further comprising the following steps:
 D. checking, in relation to said energy efficiency determined in step C, if a first derivative of the pressure signal is lower than a first maximum threshold value throughout the entire heartbeat into consideration and if the second derivative is lower than a second maximum threshold value throughout the entire heartbeat into consideration and in a negative case executing step E, otherwise, executing step F;   E. selecting a cutoff frequency of a low-pass filter on the basis of the energy efficiency determined in step C, of the first derivative and the second derivative, and applying said low-pass filter to the pressure signal, obtaining a new sampled pressure signal, and executing the previous steps starting from step B;   F. providing, as exit signal, the pressure signal on which the step B has been executed for the last time.   
     
     
         3 . A method according to  claim 1 , wherein said one or more resonance points are determined in step B by the following sub-steps:
 determining a total number of points of relative maximum of the first derivative of the pressure signal (sampled) in a range of a single heartbeat;   determining the points of relative maximum of the second derivative of the pressure signal in the range of a single heartbeat; and   determining the points of relative maximum of the second derivative having highest values and determining the time instants in which said highest values occur, considering the points of the pressure signal in said time instants as resonance points.   
     
     
         4 . A method according to  claim 1 , wherein, in the step B, the following characteristic points of the pressure signal are determined:
 the point of initial diastolic pressure;   the point of sistolic pressure;   the dicrotic point; and   one or more resonance points.   
     
     
         5 . A method according to  claim 2 , wherein said first maximum threshold value and said second maximum threshold value depend on the energy efficiency determined in step C. 
     
     
         6 . A method according to  claim 2 , wherein, in said step D, checking whether said energy efficiency determined in step C belongs to one of three or more adjacent variability intervals, the first maximum threshold value and said second maximum threshold value depending on the interval to which the energy efficiency determined in step C belongs. 
     
     
         7 . A method according to  claim 6 , wherein, in said step E, the cutoff frequency is selected as follows:
 energy efficiency values are discriminated in three or more adjacent intervals of variability;   for each of said three or more adjacent intervals of variability of the energy efficiency determined in step C, the values of said first derivative of the pressure signal in the whole heartbeat are discriminated in three or more adjacent intervals of variability; and   for each of said variability intervals of the first derivative of the pressure signal in the whole heartbeat, the values of the second derivative of the pressure signal are discriminated into three or more not superimposed variability intervals to which corresponds a respective value of said cut-off frequency.   
     
     
         8 . A method according to  claim 2 , wherein said cutoff frequency increases as the first derivative of the pressure signal increases, with the energy efficiency and the second derivative of the pressure signal being constant. 
     
     
         9 . A method according to  claim 2 , wherein said cutoff frequency decreases as the second derivative of the pressure signal increases, with the energy efficiency and the first derivative of the pressure signal being constant. 
     
     
         10 . A method according to  claim 2 , wherein said cutoff frequency is variable between 0.5 Hz and 10 Hz. 
     
     
         11 . A method according to  claim 2 , wherein in step F the pressure signal is shown on a display. 
     
     
         12 . A method according to  claim 1 , wherein in step C the energy efficiency value is shown on a display. 
     
     
         13 . An automatic apparatus for processing blood pressure signal, the apparatus comprising:
 processing means for executing the steps of a method comprising the steps of:
 A. sampling a detected pressure signal for one or more heartbeats, each heartbeat starting at an initial instant coinciding to that of an initial diastolic pressure and ending at a final instant coinciding to that of subsequent diastolic pressure and comprising a dicrotic point, each heartbeat having a systolic phase comprised between the initial diastolic point and the dicrotic point; 
 B. automatically analyzing and discriminating a morphology of the sampled pressure signal for each heartbeat, determining an instant and pressure value of one or more characteristic points of the pressure signal selected from one or more of a point of initial diastolic blood pressure, a point of systolic pressure, a dicrotic point and one or more resonance points, each of which occurs when a second derivative of the pressure signal has a relative maximum, wherein at least a characteristic point of the pressure signal belongs to the systolic phase of the heartbeat and is different from the point of initial diastolic pressure; and 
 C. for each heartbeat determining an energy efficiency value through the following sub-steps:
 determining a direct dynamic pressure wave impedance for each of said one or more characteristic points belonging to the systolic phase of the heartbeat into consideration with an exception of the point of initial diastolic pressure, said direct dynamic pressure impedance being given by a ratio between a value of the pressure signal in the characteristic point and a distance of the instant from the initial instant of the heartbeat into consideration, and determining an impedance of a direct pressure wave by adding with alternating signs the values of the dynamic direct impedances ordered according to a direct temporal order starting from the initial instant of the heartbeat into consideration up to the dicrotic instant, applying a positive sign to the first dynamic direct impedance according to the direct temporal order; 
 for each of said one or more characteristic points determining a dynamic reflected impedance that is given by the ratio between the pressure at the characteristic point and the distance of the respective instant from the instant of a final beat, and determining the value of an impedance of reflected waves of pressure is obtained by adding the dynamic impedances with alternating signs of the second set of points thus determined, sorted according to a reverse temporal order starting from the instant of the final beat to the instant of the initial diastolic pressure, giving a positive sign to the first dynamic impedance according to the reverse temporal order; and 
 determining said energy efficiency as the ratio between the impedance of the direct wave pressure and the impedance of the reflected waves. 
 
   
     
     
         14 . A computer program, comprising coded means for executing, when operating in connection with processing means of an apparatus, the steps of a method comprising the steps of:
 A. sampling a detected pressure signal for one or more heartbeats, each heartbeat starting at an initial instant coinciding to that of an initial diastolic pressure and ending at a final instant coinciding to that of subsequent diastolic pressure and comprising a dicrotic point, each heartbeat having a systolic phase comprised between the initial diastolic point and the dicrotic point;   B. automatically analyzing and discriminating a morphology of the sampled pressure signal for each heartbeat, determining an instant and pressure value of one or more characteristic points of the pressure signal selected from one or more of a point of initial diastolic blood pressure, a point of systolic pressure, a dicrotic point and one or more resonance points, each of which occurs when a second derivative of the pressure signal has a relative maximum, wherein at least a characteristic point of the pressure signal belongs to the systolic phase of the heartbeat and is different from the point of initial diastolic pressure; and   C. for each heartbeat determining an energy efficiency value through the following sub-steps:
 determining a direct dynamic pressure wave impedance for each of said one or more characteristic points belonging to the systolic phase of the heartbeat into consideration with an exception of the point of initial diastolic pressure, said direct dynamic pressure impedance being given by a ratio between a value of the pressure signal in the characteristic point and a distance of the instant from the initial instant of the heartbeat into consideration, and determining an impedance of a direct pressure wave by adding with alternating signs the values of the dynamic direct impedances ordered according to a direct temporal order starting from the initial instant of the heartbeat into consideration up to the dicrotic instant, applying a positive sign to the first dynamic direct impedance according to the direct temporal order; 
 for each of said one or more characteristic points determining a dynamic reflected impedance that is given by the ratio between the pressure at the characteristic point and the distance of the respective instant from the instant of a final beat, and determining the value of an impedance of reflected waves of pressure is obtained by adding the dynamic impedances with alternating signs of the second set of points thus determined, sorted according to a reverse temporal order starting from the instant of the final beat to the instant of the initial diastolic pressure, giving a positive sign to the first dynamic impedance according to the reverse temporal order; and 
 determining said energy efficiency as the ratio between the impedance of the direct wave pressure and the impedance of the reflected waves. 
   
     
     
         15 . A memory support readable by computer means, the memory comprising a program, said program comprising coded means for executing, when operating in connection with processing means of an apparatus, a method comprising the steps of:
 A. sampling a detected pressure signal for one or more heartbeats, each heartbeat starting at an initial instant coinciding to that of an initial diastolic pressure and ending at a final instant coinciding to that of subsequent diastolic pressure and comprising a dicrotic point, each heartbeat having a systolic phase comprised between the initial diastolic point and the dicrotic point;   B. automatically analyzing and discriminating a morphology of the sampled pressure signal for each heartbeat, determining an instant and pressure value of one or more characteristic points of the pressure signal selected from one or more of a point of initial diastolic blood pressure, a point of systolic pressure, a dicrotic point and one or more resonance points, each of which occurs when a second derivative of the pressure signal has a relative maximum, wherein at least a characteristic point of the pressure signal belongs to the systolic phase of the heartbeat and is different from the point of initial diastolic pressure; and   C. for each heartbeat determining an energy efficiency value through the following sub-steps:
 determining a direct dynamic pressure wave impedance for each of said one or more characteristic points belonging to the systolic phase of the heartbeat into consideration with an exception of the point of initial diastolic pressure, said direct dynamic pressure impedance being given by a ratio between a value of the pressure signal in the characteristic point and a distance of the instant from the initial instant of the heartbeat into consideration, and determining an impedance of a direct pressure wave by adding with alternating signs the values of the dynamic direct impedances ordered according to a direct temporal order starting from the initial instant of the heartbeat into consideration up to the dicrotic instant, applying a positive sign to the first dynamic direct impedance according to the direct temporal order; 
 for each of said one or more characteristic points determining a dynamic reflected impedance that is given by the ratio between the pressure at the characteristic point and the distance of the respective instant from the instant of a final beat, and determining the value of an impedance of reflected waves of pressure is obtained by adding the dynamic impedances with alternating signs of the second set of points thus determined, sorted according to a reverse temporal order starting from the instant of the final beat to the instant of the initial diastolic pressure, giving a positive sign to the first dynamic impedance according to the reverse temporal order; and 
 determining said energy efficiency as the ratio between the impedance of the direct wave pressure and the impedance of the reflected waves. 
   
     
     
         16 . A method according to  claim 2 , wherein said cutoff frequency is variable between 2 Hz and 80 Hz. 
     
     
         17 . A method according to  claim 2 , wherein said cutoff frequency is variable between 3 Hz and 60 Hz.